05000267/LER-1979-049, Forwards LER 79-049/03L-0

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Forwards LER 79-049/03L-0
ML19210D087
Person / Time
Site: Fort Saint Vrain Xcel Energy icon.png
Issue date: 11/13/1979
From: Warembourg D
PUBLIC SERVICE CO. OF COLORADO
To: Seyfrit K
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19210D088 List:
References
NUDOCS 7911200511
Download: ML19210D087 (15)
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LER-1979-049, Forwards LER 79-049/03L-0
Event date:
Report date:
2671979049R00 - NRC Website
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text

.

1, public service company ce cdwado 16805 Weld County Road 191/2, Platteville, Colorado 80651 November 13, 1979 Fo rt S t. Vrain Unit No. 1 P-79273 Mr. Karl V. Seyfrit, Director Nuclear Regulatory Commission Region IV '

Office of Inspecti.,

2d Enforcement 611 Rye.a Plaza Drive Suite 1000 Arlington, Texas 76012 REF: Facility Operating License No. DPR-34 Docket No. 50-267

Dear Mr. Seyfrit:

Enclosed please find a copy of Reportable Occurrence Report No. 50-267/79-49/03-L-0, Final, submitted per the requirements o f Technical Specification AC 7.5.2(b)4.

Also, please find enclosed one copy of the Licensee Event Report for Reportable Occurrence Report No. 50-267/79-49/03-L-0.

Very truly yours, WW Don Warembourg v Manager, Nuclear Production DW/alk cc: Director, MIPC

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4 7011200 S

REPORT DATE:

Novembe r 13, 1979 REPORTABLE OCCURRENCE 79-49 ISSUE O OCCURRENCE DATE:

Octob er 14, 1979 Page 1 of 14 FORT ST. VRAIN NUCLEAR GENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO 16805 WELD COUNTY ROAD 19 1/2 PLAITEVILLE, COLORADO 80651 REPORT NO. 50-267/ 79-49 /03-L-0 Final IDENTIFICATION OF OCCURRENCE:

On October 14, 1979, an upset in the circulator buffer helium system caused a release of activity both in the reactor building and out the reactor building ventilation exhaust stack.

This is being reported at the request of the Inspection and Enforcement Resi-dent Inspector under the provisions of Fort St. Vrain Technical Specification AC 7.5.2(b)4.

CONDITIONS PRIOR TO OCCURRENCE:

S teady S tate Power The major plant parameters at the time of the event were as follows:

Reactor Power 531 MJth Electrical Power 200 MWe Secondary Coolant Pressure 2,445 psig Secondary Coolant Temperature 1,0 00

  • F Secondary Coolant Flow 1,400 K#/hr.

Primary Coolant Pressure 647 psig Primary Coolant Core Inlet Temperature 682

  • F Primary Coolant Core Outlet Temperature 1,315
  • F Primary Coolant Flow 2,635 K#/hr.

Circulator lA 7,400 RPM Circulator 1B 7,400 RPM Circulator 1C 7,400 RPM Circulator ID 7,400 RPM 13/3

'33

REPORTABLE OCCURRENCE 79-49 ISSUE 0 Page 2 of 14 DESCRIPTION OF OCCURRE1CE:

Time Descriotion 0315 Buffer helium dryer swapped from "A" to "B" tower and cross-tower leakage was indicated by an increase in low pressure separator pressure.

0400 Began reducing power in preparation for bypassing buffer helium dryer to prevent moisture / oxidant problems.

Re-actor power approximately 63%.

0500 Reactor power approximately 59%.

0600 Reactor power approximately 50%.

App roximately 0630 Reduced buffer helium supply and return flows to 5.8 and 3.0 ACFM, respectively. Bypassed buffer helium dryer by opening HV-2152. PDIS-2152 indicated approximately 2 psid across dryer (normal).

Ran approximately 15 min-utes with this lineup and no buffer helium upset.

Ap proximately 0645 Shut V-21113 (dryer inlet block) and shut V-21615 (dryer outlet block) to isolate dryer. Also isolated purge line to dryer by shutting V-211450, shutting needle valve V-211641, and f ailing FCV-2151 shut (pne umatic).

Started to open V-211413 and simultaneously close inlet block to HV-2152. Ran for approximately two minutes this way and then FV-2339 (purified helium compressor recircu-lation flow), PDV-2367-2 (buffer helium from purification system), and PDV-23111 (purified helium to PCRV relief valve penetration) began to hunt. ?DV-2367-2 was hunting through its full cycle. Reactor operator placed PDV-2367-2 and PDV-23111 in manual to s top the hunting. Bu f-fer supply did not stabilize so reactor operator returned PDV-2367-2 and PDV-23111 to automatic control.

0649 Reactor operator placed FC-2167 (buffer supply to "A" circulator) in manual to stabilize buffer supply flow.

" A" circulator buf fer-mid-buffer (BMB) dif ferential pres-sure was cycling from about +70 ' water to about +17" water.

"A" circulator shortly af terwards tripped on buffer-mid-buffer high at +80" water. Brake and seal set fo r " A" circulator automatically. This prevents loss of primary coolant down shaft of "A" circulator.

0650 FV-2339, PDV-2367-2, and PDV-23111 still cycling. P DV-2367-2 cycling full range.

0652 "D" circulator tripped on buffer-mid-buffer high. Brake and c.eal set for "D" circulator automatically.

j2 i7

,Jl3 s,

REPORTiBLE OCCURRENCE 79-49 ISSUE O Page 3 of 14 Time Des crio tion App roximately 0656 Purified helium compressor (FHC) tripped.

This was prob-ably caused by the cycling of FV-2239, PDV-236 7-2, and PDV-23111 which either caused a low purified helium flow (less than 18 ACEM) or a high compressor differential pressure (greater than 42 psid). S tandby purified helium compressor did not start (start inhibited if purified helium compres-sor differential pressure is greater than 10 psid).

Approximately 0656 to 0658 Tried to get purified helium compressors started. Kept tripping due to high purified helium compressor differen-tial pressure / low flow.

During this time primary coolant was coming down the shaf ts of "B" and "C" circulators and entering circulator auxili-aries as follows:

Discharce to Stack 1.

It is not known for certain if the low pressure separator gas relief lif ted at 50 psig. This relief is vented to the reactor building stack via the reactor building exhaust filters.

It is in a com=on line with the helium dryer outlet knock-out pot which also has a 50 psig relief (V-211266).

This relief also relieves to the reactor building exhaust system and subsequently to the stack.

The possible pressurization path of the low pres-sure separator would be from the buffer helium dryer purge line as follows:

a.

When the buffer helium dryer swapped from tower "A" to tower "B", the "B" tower purge valves shut (HV-21348 and HV-21352).

b.

Leakage past the seat of HV-21352 flows through cooler E-2102X and V-21524, to the dryer knock-out pot, and then the low pressure separator increasing low pressure separator pressure.

c.

Leakage via this path was occurring as in-dicated by increasing pressure in the low pressure separator.

Cross-tower leakage was verified in the control room by this method.

1373

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REPORTABLE OCCURRENCE 79-49 ISSUE O Page 4 of 14 Time

Description

App roximately 0656 to 0658d.

Note that at about 0620 RT-31193 began to in-crease indicating contaminated low pressure separator water. This increase slowly con-tinued until the low pressure separator drains were directed to the liquid waste sump at about 0700.

2.

Helium / water drains were discharged from the cir-culator to the high pressure separator, to the buffer helium recirculators, through vent valve V-211413 to the reactor building stack.

3.

Circulator main bearing water drains discharged to the bearing water surge tanks, through an equilizing line to the suction of the recircula-tors and through V-211413 to the reactor building s tack.

4.

S team / water drains discharged from circulators to low pressure separator, to helium recovery com-pressors (RIX), through vent HV-21334-1, to the reactor building stack.

These four possible vents to the reactor building stack caused RT-7324-1 monitor to trip (trips at 77,000 cpm).

Within approximately 30 seconds, the reactor operator walked behind the panel observed that RIS-7324-1 was reading less than 100 cpm, and reset the RT.

No other alarms from this RT were received.

Discharge to Reactor Building Contaminated water in low pressure separators caused RT-21251 to trip, stopping the bearing water removal pumps and diverting lcw pressure separator drains to liquid waste sump via 1" drain line. Liquid waste sump was pumped to the liquid waste tank. Diminished draining capacity via 1" line allowed level in low pressure separator to increase, causing gas in low pressure separator to compress and lif t the interstage reliefs an the RIX compressor at approximately 15 psig.

This released contaminated helium to reactor building.

Persons in the area observed the TRITON monitor re-spond as the RIX interstage reliefs lif ted.

0700 Reactor power 39.7%.

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REPORTABLE OCCURRENCE 79-49 ISSUE O Page 5 of 14 Time Des crip tion App roximately 0700 Af ter it became apparent the purified helium compressors would not stay on, reactor operator cut in high pressure helium bottles from storage to supply buffer helium via HV-2166-2.

The bottles were in service approximately 1 to 2 minutes. They did not appear to re-establish stable buffer helium supply, so the reactor operator secured high pressure bottles.

Both standby recirculators s tarted automatically.

Reac-tor operator secured standby recirculators.

Approximately 0705 Personnel opened inlet block to HV-2152, then shut v-211413 vent. This returned buffer helium lineup to nor-mal with the exception of bypassing the buffer helium dryer.

Approximately 0708 Reactor operator started a purified helium compressor.

Buffer helium supply and return stablilized to "B" and "C" circulators.

Approximately 0770 Reactor building sump pumps were placed in " pull-to-lock".

Liquid waste tankc full. Low pressure separator drains were directed to the deaerator.

RT-31193 tripped at 500 cpm, reached a maximum of 800 cpm, and then decreased.

App roximately 0720 Reactor power decrease was initiated from approximately 26%.

Going to less than 2%.

0800 Main turbine generator tripped on low steam temperatures.

0900 Reactor Power 18.5%.

1000 Reactor power 8. 8%.

1000 RT-31193 on SJAE reset at less than 500 cpm.

1030

" A" and "D" circulators to self-turbining.

1100 Reactor power 6.1%.

! 3 / 3

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c REPORTABLE OCCURRENCE 79-49 ISSUE O Page 6 of 14 Time

Description

1130 Helium dryer returned to service; "B" tower in service, "A"

tower at 60 psig.

FCV-2151, V-211450, V.-211641 all closed in purge line. Normally open valve V-21524 was lef t open because it cannot be reached in a Scott Air P ack.

1200 Reactor power 2. 7%.

1300 Reactor power 1.9%.

1700 Low pressure separator activity less than 10,000 cpm.

Res et RT-21251.

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REPORTABLE OCCURRENCE 79-49 ISSUE 0 Page 7 of 14 High es t j[r Time Uo Counts Alarmed Remarks 5

21251 0700 10 Yes (10,000)

Low pressure separator dr ains to liquid waste sump.

6314-2 0215 60,000 No (2,300,000)

T-62 vent noble gas (unrelated to this event).

2263 0700 2,000 Yes (600)

Purg low pressure separator to deaerator.

2264 0700 300 No (570)

Pump low pressure separator to deaerator.

6212 0 700 500 No (1,050)

Dissolved noble gases.

6213 0700 900 Yes (800)

Dissolved noble gases.

31193 0700 800 Yes (500)

Pump low pressure separator to deaerator.

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4 REPORTABLE OCCURRENCE 79-49 ISSUE 0 Page 8 of 14 Radiological Calculations Conditions Tica of Release - Approximately 5 minutes 8.3E-2 hours

=

Exhaust Stack Flow - 32,000 cfm = 9.06E+8 cc/ min = 1.51E+7 cc/see Wind Speed - 10 mph Wind Direction - 245* (SW)

S tability Category - D Noble Gas 1.

Noble gas released as indicated on RT-4802 (FING):

Maximum Count Rate - 1,300 cpm Average Count Rate - 650 cpm Sensitivity - 3. 70E-8uCi/cc/ cpm Maximum Concentration in Stack - 4.85E-5 pC1/cc Average Concentration in Stack - 2.43E-5 uC1/cc Noble Gas Released = (2.43E-5uci/cc)(9.06E + 8 cc/ min)(5 min)

= 1.10E+5 uC1

= 0.11 Ci noble gas released 2.

% of Technical Specification Limit = (release rate)(

" ) (100%)

gp 3E+10

= (1.51E+7 cc/sec)( f{_' ci c 5

) (100%)

3E+10

= 61.2%

3.

Incident Dose at EAB 1//Z

'J/J

) l, J (Q) (T) (SD)/u D

=

where:

D incident dose

=

Q source term

=

T exposure time

=

REPORTABLE OCCURRENCE 79-49 ISSUE 0 Page 9 of 14 3.standard dose factor (FSV Emergency procedure based SD

=

on release of 1 C1/sec,1 mph wind,1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> exposure to noble gas) wind speed u

=

Q = (2.43E-5uci/cc)(1.51E+7 cc/sec)

= 3.67E+2 uCi/sec

= 3.67E-4 C1/sec Re h

D = (3.67E-4 C1/sec)(8. 3E-2 hr)( 6E-3

)

C g

10 mph 1.8E-8 Rem

=

1 I as Indicated by RT-7325-1 Cartridge Cartridge I activity = 8.61E-6uci/ cartridge 1.

I released = (s tack flow) (cartridge activity) sample flow

= ( 32,000 cfm) (8. 61E-6uC1) 1.4 cfm

=.197 uCi released 2.

% of Technical Specification Limit "5

(1. 51E+7 cc/sec) (7,43E]13 cc*) (100%)

=

3E+10

= 15.3%

! b / J'

>,J 700 31 3.

I Incident Dose at EAB Q =.197E-6 Ci 6.56E-10 C1/sec

=

300 see D = (0) (T)(SD) u (6. 56E-10 Ci/sec)(8. 3E-2 hr)(76

)g )

=

10 mph

= 4.13E-10 Rem

REPORTABLE OCCURRENCE 79-49 ISSUE O Page 10 of 14 Reactor Building CAM EL 4740 4.15E-8 pCi/cc beta particulate Concentration remained relatively constant until 1220, then started to decrease.

At 1700 concentration was 1.7E-10 pCi/cc beta particulate No significant activity was found in the turbine building.

Environmental samples analy::ed by CSU (10-16-79) showed no significant acti-vity above background.

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REPORTABLE OCCURRENCE 79-49 ISSUE O Page 11 of 14 CALCULATION OF DOSE RECEIVED BY HEALTH PHYSICS TECHNICIAN 10-14-79 NOTE: Pocket dosimeter worn during exposure period showed 0 mr.

1.

Particulate activity from Beta particulate CAM elevation 4 740 4.15E-8 pC1/cc.

2.

From previous releases into the building it has been determined that the radionuclides present are 88Kr, 13a Xe, and 133Xe, and daughters.

3.

Assumptions a.

The particulates are in equilibrium with the precursor, b.

The dese is made up of exposure from Kr, Xe, and Xe.

The activity detected is the sum of the particulate activities from c.

1 33 Xe and 8 Kr daughters.

13fr = 2.08E-8 pCi/cc Xe = 2.08E-8 pC1/cc 133 d.

Xe is present at a concentration of 2.08E-8 uC1/cc.

e.

One year's exposure time = 2,080 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.

4.

Reference Regulatory Guide 1.109, Table B-1.

5.

Whole Body Dose Received by individual exposed 2.68 hours7.87037e-4 days <br />0.0189 hours <br />1.124339e-4 weeks <br />2.5874e-5 months <br />.

6.

From S tep 4 above Dose Factor for Exposure Kr 1.47E-2 (mrem-m )/(o Ci - year)

Xe

8. 83E-3 (mrem-m )/ (pCi - year)

Xe

2. 9 4E-4 (mrem-m ) / (p Ci - y ear) 7.

Dose rate (mres/ hour)

=

(2.08E-8 uCi/cc) ( l year )

2080 Hrs (Dose Factor mrem / year /pCi/m )

=

(IE-12 pCi/cc/oCi/m )

4 Kr (IEl)(1.47E-2) 1.47E-1 mrera/ hour

=

138Xe (IE1) (8. 83E-3) 8.83E-2 mrem / hour

=

133Xe (lEl)(2.94E-4) 2.94E-3 mres/ hour

=

Total dose rate 2.38E-1 mrem / hour

=

8.

Total Dose (2.68 hours7.87037e-4 days <br />0.0189 hours <br />1.124339e-4 weeks <br />2.5874e-5 months <br /> exposed)(2.38E-1 mrem / hour) 6.38E-1 crem.

=

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REPORTABLE OCCURRENCE 79-49 ISSUE O Page 12 of 14 APPARENT CAUSE OF OCCURRENCE:

Cross-tower leakage in the bufter helium dryer due to a leaking valve, HV-21352.

ANALYSIS OF OCCURRENCE:

The problem with the dryer valves has existed for quite awhile. Various at-tempts have been made to fix this dryer, but have been unsuccessful so far.

The valve seats are a teflon material which has either been too soft and unable to take the temperatures encountered or too hard and subject to cracking during valve operations. When this occurrence started, due to dryer cross-tower leakage, instrumentation personnel expected to temporarily bypass the buffer helium dryer and repair the leaking regeneration valve. A temporary system operating procedure deviation was prepared and the job started. At ap-proximately 0645 hours0.00747 days <br />0.179 hours <br />0.00107 weeks <br />2.454225e-4 months <br /> (see event description) an upset in the buffer helium system occurred that could not be restabilized until af ter two circulators had tripped and activity had been released to the reactor building and the plant exhaust stack. There was no evidence of improper or inadequate plant operation or job planning during this evaluation. All plant personnel involved responded proparly in attempting to restore the circulator's buffer helium auxiliary sys-tem to a stable condition.

CORRECTIVE ACTION:

The committee investigating this occurrence made several recommendations as follows:

Place RT's on continuous recorders. At present, a plotted point every five minutes is inadequate.

RT-21251 needs to have flushing capability. At present when the bearing water removal pu=ps are tripped, the monitoring leg f or the RT is static and thus not representative of the low pressure separator activity.

Investigate possibility of automatically isolating quench water to the low pressure separator when RT-21251 trips. This may prevent an in-creasing separator level and lessen the chances of RIX reliefs lifting.

Investigate possibility of bypassing buffer helium return to purification system just downstream of V-2383.

Direct flow to on service purification system dryer by placing manual bypass valve around HV-2305 or HV-2306.

Dryers would need regeneration more of ten if this path were used but it would save a lot of helium and eliminate one major flow path of contaminated helium up the stack.

Investigate possibility of shutting buffer supply and return valves for the operating circulators af ter loss of buffer helium. This would lock in primary coolant inside circulator and minimize escape (assuming no loss of bearing water below normal cavity levels).

I373

?

REPORTABLE OCCURRENCE 79-49 ISSUE O Page 13 of 14 CORRECTIVE ACTION (continued) :

Besides investigating these recommendations several actions have been taken to reduce the problems with the buffer helium system and in case of an upset to reduce the possibility of affecting the bearing water system or releasing activity from the buffer system. These are being done under Change Notice 990 and include an automatic drain on the buffer dryer knoc-kout pot, an automatic isolation valve on the line from dryer purge to low pressure separator which isolates on high pressure or high activity 1:: thelow pressure separator. Also an automatic drain line from the helium recovery compressors knockout pots, and the vent and relief valves from the low pressure separator and buffer he-lium dryer are routed to the reactor building ventilation exhaust stack by this change notice.

FAILURE DATA /SIMILAR REPORTED OCCURRENCES :

Reportable Occurrence Report No. 50-267/79-43.

PROGRAMMATIC IMPACT:

None CODE IMPACT:

l}/}

None

REPORTABLE OCCURRENCE 79-49 ISSLT 0 Page 14 of 14 Prep red by:

A M B. Reed

/

Technical Services,Tey5inician

/

i Reviewed by:

6 rf 2.

ahm Te ical Services Supervisor Reviewed by:

Frank M. Mathie Operations Manager Approved by:

7touMW L

Don Warembourg

/

Manager, Nuclear Production 1373 El f

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